This invention relates to a self-scuttling, buoyant pyrotechnic marine marker.
Pyrotechnic markers are used as signalling devices for example for long range marine patrol aircraft in conjunction with sonobuoys during anti-submarine operations. They also may be used for search and rescue operations, for example to mark a wreckage sight or survivors in the water, or to mark a location where equipment has been dropped into the water so that the equipment can be located by boats or ships operating on the water surface. Heretofore, in coastal regions, although these markers are dropped out at sea where a majority of them sink by taking in water after they have fulfilled their intended function, a substantial number have been washed ashore.
The pyrotechnic candle, usually enclosed in an elongated jacket, may consist predominantly of red phosphorus which produces dense white smoke and a yellow flame for a period of 13 to 19 minutes from time of ignition by a salt water-activated battery and squib combination. A typical composition of such a candle is as follows:
______________________________________ Parts by Weight ______________________________________ RED PHOSPHORUS 50.0 .+-. 5.0 LINSEED OIL 3.0 .+-. 0.3 ZINC OXIDE 3.0 .+-. 0.3 MAGNESIUM POWDER 7.0 .+-. 1.0 MANGANESE DIOXIDE 34.0 .+-. 2.0 ______________________________________
Although the marker initially floats vertically in the water, the increase in positive buoyancy after several minutes of burning causes it to cant until, as the burning continues, the marker usually finally ceases burning in an almost horizontal position on the surface of the water. While many of these markers take in water while in this position and eventually sink with the aid of normal wave action, an insulable residue has often built up in and blocked the smoke or flame emission hole of spent phosphorus markers, preventing water entry with the result that such markers often do not sink when spent, and drift to shore.
Where such pyrotechnic candle is made of phosphorus, unburned phosphorus, capable of re-igniting spontaneously when dry, may remain inside such markers washed ashore, thus presenting a potential hazard to curious persons finding and handling them. Scuttling of such markers is therefore desirable to eliminate both a potential hazard and a contributor to shore line pollution.
It has been suggested in the course of research conducted to overcome such problems and provide a self-scuttling marker, that a dissolvable plug be used to provide a readily available path for water entry into the marker. None of the materials examined was found to be satisfactory because of difficulties with adhesion to the jacket of the marker or because of shrinkage of the plug during curing and an unacceptably slow rate of dissolving.
It has been alternatively suggested to provide fusible plugs in the jacket of the marker, which plugs would melt due to the rise in temperature inside the marker caused by the burning composition. Plugs of beeswax and paraffin wax were found to be not strong enough to withstand initial pressure built up inside the marker upon ignition of the starter mix. Alloys having a low melting point, such as Wood's metal (melting point 158.degree. F.), were also investigated. While found to be effective in some circumstances resulting in improved sinkage rates of the markers, such plugs experienced excessive external cooling in the presence of cold water temperatures, which adversely affected their ability to melt. Also, residues were produced during burning of the candle which, in cold water, tended to solidify and replug the hole vacated by the melted plug.
Accordingly, it is an object of the present invention to provide a self-scuttling marker which is reliable in a variety of circumstances and which is economical and simple to produce, with few components and manufacturing operations.